The present invention relates to a method for controlling a drive arrangement in a watercraft, comprising: detecting thrust and steering commands from an operating device which is connected to a control unit; controlling said drive arrangement based on detected commands from said operating device, for obtaining a desired course of travel of the watercraft, wherein a force is generated which acts towards a defined position on said watercraft; and determining the speed of the watercraft.
The invention also relates to an arrangement for controlling a drive arrangement in a watercraft, comprising: an operating device for detecting thrust and steering commands; a control unit being arranged for controlling said drive arrangement based on detected commands from said operating device, for obtaining a desired course of travel of the watercraft, said control unit being arranged for generating a force which acts towards a defined position on said watercraft; a speed detector for determining the speed of the watercraft.
When controlling a watercraft, for example in the form of smaller ships and leisure boats, there is a general need for arrangements which allow a precise control of the thrust and steering of the watercraft. In particular, there is a need for a arrangements providing accurate control of the watercraft during docking. In this regard, the term “docking” refers to a maneuver in which a watercraft is propelled towards a harbor, marina or pier in order to be landed and secured.
In certain situations, the docking maneuver can be quite difficult for the driver of the watercraft, for example when the watercraft must be landed with one of its sides towards the harbor, for example in a space between two other boats. Such a situation can be simplified if the watercraft is arranged to be propelled in the sideways direction, i.e. in a direction which is generally transverse to the longitudinal direction of the watercraft.
Such a sideways movement of a watercraft can be carried out if the watercraft is provided with two drive arrangements which are separately controllable, i.e. independently of each other. The drive arrangements can for example be in the form of conventional combustion engines which are connected to propellers. By shifting one of the engines into reverse and operating the other engine in forwards drive, while at the same time carefully adjusting the steering angles of the two propellers, the watercraft can be brought to move in a direction which is essentially transverse to its longitudinal direction.
A similar type of docking maneuver can also be obtained in watercraft provided with bow thrusters or stern thrusters. A bow thruster comprises a propeller which is mounted in the bow, generally transverse to the longitudinal direction of the watercraft, in order to generate a side force on the bow. In this manner, the watercraft can be more easily controlled when docking or maneuvering at low speeds. A similar arrangement, a so-called stern thruster, can be provided in the stern of a watercraft.
As mentioned above, it is important to be able to control the watercraft in a manner so that it may travel correctly in the sideways direction, i.e. transverse to the longitudinal direction of the watercraft, during a docking maneuver. In order to obtain this desired course of travel, the drive arrangement can be controlled so that the sum of forces acting on the watercraft acts upon a specified position corresponding to the center of gravity of the watercraft. Assuming that the speed of the watercraft is relatively low, this will normally lead to a situation wherein the watercraft moves in a straight sideways direction.
However, during a docking maneuver, the movements of the watercraft may sometimes deviate from a perfect sideways direction. For example, the watercraft may assume a direction of travel which follows a curved path, which obviously is a disadvantage. Such a situation may for example be due to a rotating torque acting on the watercraft when travelling.
Consequently, an intention of steering a watercraft along a course which is transverse to the longitudinal direction of the watercraft may in fact lead to a curve-shaped course of travel of the watercraft For this reason, there is a demand for arrangements and methods in which such a tendency to rotate can be eliminated.
An object of the present invention is to provide a method and arrangement for operating a drive arrangement in a watercraft, by means of which the above-mentioned problem can be solved so that an accurate course of travel of a watercraft can be provided, in particular during docking of the watercraft.
This object is obtained by means of a method as initially mentioned, wherein said method furthermore comprises adapting said position on which the force from said drive arrangement acts as a function of at least said speed and as a function of the influence of the position of the center of pressure of said watercraft, thereby maintaining said desired course of travel.
The object is also obtained by means of an arrangement as initially mentioned, in which said control unit is arranged for adapting said position on which the force from said drive arrangement acts as a function of at least said speed and as a function of the influence of the position of the center of pressure of said watercraft, thereby maintaining said desired course of travel.